Starches modified with n-vinyl compounds

ABSTRACT

MODIFIED STARCH PRODUCTS POSSESSING LABILE SUBSTITUENT GROUPS ARE PRODUCED BY REACTING A STARCH BASE WITH NVINYL AMIDO OR N-VINYL IMIDO COMPOUNDS WHEREIN THE NITROGEN TO WHICH THE VINYL GROUP IS ATTACHED IS ADJACENT TO AT LEAST ONE CARBONYL GROUP. THE REACTION IS CARRIED OUT UNDER CONTROLLED CONDITIONS AND, OPTIONALLY, IN THE PRESENCE OF A NETURAL SALT. THE RESULTING INHIBITED AND STABILIZED STARCH PRODUCTS ARE USEFUL AS THICKENERS, BINDERS, AND DUSTING POWDERS.

United States Patent 3,775,400 STARCHES MODIFIED WITH N-VINYL COMPOUNDSOtto B. Wurzburg, Whitehouse Station, and Wadym Jarowenko, Plaiufield,N.J., assignors to National Starch and Chemical Corporation, New York,N.Y. No Drawing. Filed Oct. 3, 1972, Ser. No. 294,551 Int. Cl. C08b19/04 US. Cl. 260-233.3 R 11 Claims ABSTRACT OF THE DISCLOSUREBACKGROUND OF INVENTION This invention relates to a novel method for thepreparations of inhibited and stabilized starch products and to theproducts produced thereby.

The term stabilized starch refers to a starch in which the tendency tocongeal is reduced. Such stabilized starches exhibit an enhancedtendency to swell when cooked in aqueous suspension to form stablecolloids with reduced tendencies to thicken, to form gels, or toseparate by syneresis. v

The term inhibited starch. refers to a starch in which 1 the granuleshave been toughened so they are more resistant to rupturing duringcooking than ordinary starch granules. Inhibited starches may exhibit areduced tendency to swell or gelatinize and generally display acomparatively short, non-cohesive consistency after cooking. The degreeof inhibition. can be controlled and varied over a wide rangeso as toproduce starches in which the tendency of the swollen granules torupture is decreased through successive stages to starch products inwhich the swelling of the granules is so highly restrained that thegranules will not swell noticeably when cooked in boiling water.

It is well known that starchmay be inhibited, while in granular form,byreaction with polyfunctional reagents such asepichlorohydrin,phosphorus oxychloride, divinyl sulfone, etc., whichcrosslink the starch molecules within the granule. This reaction resultsin the formation of covalent chemical linkages which reinforce thenormal hydrogen bonds between starch molecules which hold the granuletogether; Asa result, when the treated starch is cooked under conditionswhich normally Weaken or destroy the hydrogen bonds the granule isswollen but remains intact becausebf'these 'c'ov'alent linkages.

, Inhibited starches,are.. desired for various industrial uses. They areparticularly useful in applications where the cohesiveness and,stringiness of certain untreated starches are found to be objectionable,for example, in

various industries where 'starch products yielding short, smoothpasteson cooking are callbd for, as thickening agents Ior pastes. Highlyinhibited types are useful as surgical"dustingjpdwersl.lt lis a primeobject of this inventio'n'fto provide a novelrhethod for the preparationof modified starch produ'ctsflt' is another. object of this invention tob QYidea 'stabilized starch product. It is a further object ofi this'invention top'rovide an inhibited starch product'. lt isstill a fur'theif object of this inven- 11 tion 'to provid ea modifiedstarchproduct which is stabilized and also inhibited. Various otherobjects and advantages of this invention will become apparent from thefollowing description;

We have found that stabilized and inhibited starch products and thosehaving the combined types of modifications can be produced by reacting astarch with N- vinyl amido or irnido compounds wherein the nitrogen towhich the vinyl group is attached is adjacent to at least one carbonylgroup, under controlled conditions and, optionally, in the presence of aneutral salt catalyst. More precisely, we have discovered thatstabilized or inhibited starch products and stabilized, inhibited starchproducts may be produced by regulating the pH level within the acidicrange and the temperature of the reaction. The stabilized starchproducts are characterized by the presence of substituent groups whichare stable in neutral and alkaline media. The inhibited starch productscan be easily and controllably converted into more highly swollenproducts which are then comparable to untreated starches.

As previously indicated, the essential ingredients necessary for thepreparation of the novel starch derivatives of this invention includestarch, the N-vinyl compound and, optionally, the neutral salt.

The N-vinyl compounds useful as inhibiting and stabilizing reagentsaccording to this invention are those selected from the group consistingof N-vinylamides, N- vinyllactams, N-vinylimides, N-vinylurethanes andN- vinyloxazolidones.

The N-vinylamides suitable for our process include those compoundshaving structures represented by the following general formula:

wherein R is an alkyl group having no more than 18 carbon atoms,preferably from 2 to 6, and R is also an alkyl group, and the number ofcarbon atoms in the latter group and that of R may differ, i.e.,N-vinyl, N- methyl acetamide; N-vinyl, N-methyl acetamide; N-vinyl,N-methyl butyramide, etc.

The N-vinyllactams are represented by the following general formula:

(II) H CH;=(i1N-C=O wherein R is a methylene group and n is 2 or more,preferably from 2 to 6.

The N-vinylimide are represented by the following general formula:

wherein Ry is a phenylene group and n is 1 or Ry is a methylene groupand n is 2 or more, preferably-2.

The N-vinylurethanes suitable for our process may be those compoundshaving aliphatic or heterocyclic structures. In the instances of theformer type reagents, suitable compounds may be structurally representedas follows: 1

0H,:0N- or; p

In the instances of those reagents having heterocyclic portions,N-vinyloxazolidene compounds may'be structurally represented as follows:

I y: CH2=CN. (Ry)n-0 wherein (Ry) is as defined in Formula III, supra.

The amount of the N-vinyl compound used to react with the starch basemay vary from 0.01 to 100 percent, based on the dry weight of thestarch, depending on such factors as the starch base employed, thedegree of substitution (D.S.) desired, the particular salt catalyst, andits concentration.

Any type starch, native or converted, having a sufficient number ofhydroxyl groups available for reaction with the N-vinyl amido compoundor the N-vinyl imido compound, can be used as a base for the preparationof the inhibited or stabilized starch products of this invention.Suitable starches include, for example, corn, potato, amioca, rice,sago, tapioca, waxy maize, sorghum, wheat, and the various derivativeswhich contain a sulficient number of reactive groups. Hence, among thesuitable starches are the various starch derivatives such as ethers,esters, and thin boiling types made by known processes, for example,acid treatments, oxidative, enzymatic, or thermal degradation. Alsoincluded are the cold water swelling starches, the starch dextrins,fractions such as amylose or amylopectin, and other depolymerized starchproducts. Furthermore, it is possible, in this process, to employ agranular starch that has been partially or completely swelled by anyknown means or homogenized by subjecting it to shear. Gelatinizedstarches are also useful. Therefore our use of the term starch is seento include any amylaceous materials which possess functional groupscapable of reacting with N-vinyl compounds.

The presence of a neutral salt catalyst in the reaction system is notrequired, but such salts may be utilized to assure a more effectivestabilization or inhibition of the starch.

The mechanism by which these salts assist in the reaction is not clearlyunderstood. Nevertheless, it is presumed that they function ascatalysts. Among the applicable salts are included: alkali metalhalides, alkali metal sulfates, alkali metal nitrates, alkail metalsulfites, alkali metal nitrites, alkali metal thiocyanates,alkalineearth halides, alkaline-earth nitrates, alkaline-earth,nitrites, and alkali metal salts of organic acids such as sodiumtartrate and sodium salicylate. Thus, for the purposes of thisinvention, the term neutral salt is meant to include salts of alkalimetal and alkalineearth metals which give substantially neutral aqueoussolutions.

The exact structures of the modified starches are not known withcertainty. However, it is reasonable to assume that stabilization isafforded by the presence of the reagent groups bound to the starch bycovalent bonds. The characteristic structure of the modified portions ofthe stabilized starch will depend on the particular reagents chosen. Forexample, the modified portions of a starch obtained usingN-vinylpyrrolidone may be typically represented as follows:

which contains many anhydroglycuose units, each having three freehydroxyl groups which may react with the N-vinyl compound. Therefore,the number of such displacements or the D5. will vary with theparticular starch and reaction conditions.

In the case of the inhibited starches, however, the starch molecules maybe crosslinked by acetal groups presumably resulting from thedecomposition of the reagent when reacted in the more acidic medium. Theinhibited starch products may contain cross-linkages typicallyrepresented by the following structure:

SiO(I)HOSt CH3 wherein StO is defined as above.

In accordance with this invention, the production of a particular starchis carried out at a controlled pH between 2.0 and 7.0. At a pH between2.0 and 2.7 a predominantly inhibited product is obtained, while between2.8 and 7.0 a predominantly stabilized product is obtained. I

In general, the novel stabilization and inhibition processes of thisinvention are carried out by suspending the starch and a salt catalystin water or a water-miscible organic solvent, adding the reagent,adjusting the pH of the resultant mixture to a level between 2.0 and7.0, and then agitating the mixture 2 hours or more at temperaturesranging from about 10 C. to about 180 C. under normal orsuperatmospheric pressure depending on the temperature. The time of thereaction will depend upon reaction conditions such as the temperature,the presence of a salt catalyst and the concentration thereof. Theconcentrations of the salt, when used, and the reagent may be in excessof percent, by weight, of the starch base. The pH must be maintainedwithin the prescribed range, defined above, at all times in order toproduce the desired product. After the reaction, the suspension may beneutralized, if necessary, to a pH between 6.5 and 7.0 by the additionof a suitable base. The starch product may then be recovered byfiltering the suspension, washing the starch product essentially free ofany residual salt or other contaminants, and finally drying to amoisture constant of about 8-12 percent'of the total weight.

In the instance of the inhibition reaction granular starches are morereadily adaptable than non-granular starches. Also, since the amount ofN-vinyl compound utilized may be as small as 0.01 percent of the weightof the starch, an alternate method for the preparation of the inhibitedstarch product is afforded. In this procedure an aqueous solutioncontaining from about 10% to 50% of the N-vinyl compound having a pH ofabout 1.7 is prepared separately and is admixed with an aqueoussuspension comprising the starch based material and the neutral saltcatalyst in proportional amounts. Thereafter the reaction is achieved byagitating the resultant mixture for a period ranging from 2 up to 17hours and at pH 2.0-2.7.

In the practice of this invention it is preferred that the reactions becarried out in aqueous media by (1) suspending about 100 parts of agranular starch in about parts of water containing 15-60 parts of sodiumsulfate or magnesium sulfate; (2) admixing 3 to 50 parts of the reagent;and (3) agitating the mixture at a 'pH between 2.8 and 4.5 forstabilization and between' 2.0 and 2.7 for inhibition at a temperatureabout 25 to 40 C. for at least 2 hours.

The degree of stabilization and inhibition depends on the reactionconditions which determine number of each type of linkage. In all'cases,the starch products possess linkages which may be easily destroyed, as aresult of their sensitivity to heat and acid. These novel derivativesare characterized by their ability to yield thin, low viscositydispersions whichmay be subsequently thickened by the destruction oftheir;linkages thereby leading to swelling and ultimate rupture of theirpreviously intact granules. The characteristics of the starchderivatives may ranging from be determined by evaluating the amounts ofstabilization or inhibition by the following methods:

The amount of stabilization may be estimated by measuring the diiferencein nitrogen contents of the particular starch product prior to andsubsequent to reaction using 6 In both cases precautions were taken thatall the ingredients preceding the starch were completely dissolved priorto starch addition and the starch was uniformly suspended before addingthe reagent. Then the mixtures were agitated at about 25 C. for about 24hours. At the the Kjeldahl procedure. 5 end of this period the mixtureshad the following pHs:

The amount of granular inhibition may be estimated 11.9, 12.6. At thispoint small portions of the above by various known methods, among whichare included: samples were removed, neutralized to pH about 7, filtered,Brabender, *Brookfield, etc., viscosity measurements, washed essentiallysalt-free, and dried. Their evaluation granular swelling power (GSP)measurements, and sediby cooks and nitrogen analysis indicated little,if any, ment volume test. 10 reaction. The cooks of the samplesresembled cooks of If desired, the modified starch products of thisinvenuntreated corn starch bases of comparable viscosity. tion may alsobe prepared by means of a dry process. The remaining portions wereadjusted to pH 3.0 with In carrying out a typical dry procedure the drystarch dilute HCl or dilute NaOH and were agitated for an may first beimpregnated with the reagent solution comadditional period of 15 hours.At the end of this period pgsigg the N-lnylt;0m1tJ0U1111d in Evatcr attthe preferred tlzle reagtion rInIixtturest blag a gfihof aboifit3.0;1Tlt1ey were p y suspen ing e s arc in t e reagen so ution or a useo p a on an e s arc pro uc s recovby spraying a fine mist of the reagentsolution onto the ered by filtration, washing essentially salt-free, anddrydry starch as it is agitated. In the former method, the ing to about10-12% moisture. slurry is thoroughly mixed and thereafter dried, usingany The resulting products were evaluated using the folcommon meansdeemed suitable by the practitioner. The lowing cooking procedure andnitrogen analysis and redried mixture is then heated to between 105 and200 C. sults are listed in Table No. 1. 32.]; 30 4 331 5. fii2 i isififiififi lf ifiiiiii ii Pmedure most instances and where the highertemperatures of Into segal'ate h g l lletrie Were adged sufiicienfi thespecified range are used, heating for 15 minutes is amount? 0 Stan; an1St1 6 er to 0 tam a stare sufficlilent. thed end ofthelfreactionafaeriifortil,1 the ltreateg igz l n ii gieg to gg i g ingg g igsgg t i-"g t il ggfi starc is a owe to coo remov o e sa ts an eers organic by-products is desired, the starch is then slurried f Placeda boiling Water bath (rolling While in water, Washed and drigi agitatingcontinuously until gelatinization took place, but

If desired, the products obtained by either of the above- 8 than 5mmutes- The agltatlofl f f described procedures may Subsequently be t fid or tinued and the beakers were covered and left in the boiletherifiedusing any means suitable for such further conmg Water bath for 0tnlnutes. Then the beakers were versions well known to those skilled inthe art, including removed from the bolllng Water bath and allowed toconltrolled degradation by hydrolytic, oxidative, or therg t rookm p g tr aboltndl houtr:I 231% the ma es e resu mg coo s compare ononreae cornsc ases It is thus seen that the novel process of this invention cookedat the same time.

' TABLE N0. 1

Nit

(pe rzgi i ti Description of cold cooks at- 1 basis) D.s. pH pH 3.0

S 1 Y igf 8.1; 8.8%; Modgrately heavy salve-like sol, semi-clear. Rig ggel resembling untreated corn starch,

c rn starch 0.06 Finn set mixing to a chunky mass opaque.-." Moderatelyfirm gel somewhat chunky paste-opaque.

enables the practitioner to eifectively prepare modified starches havinglabile groups.

A large number of variations may be made in reacting the starch with thereagent by either the wet or dry procedures described above withoutmaterially departing from this invention.

Because of their unique combination of properties, the novel products ofthis invention can be utilized in many industrial applications such asthose employing suspending agents, thickeners, sizings, adhesives, andin various other applications.

The following examples will further illustrate the embodiments of ourinvention. In these examples, all parts are given by weight, unlessspecified otherwise.

EXAMPLE I This example illustrates the reactions of starch with N-vinylpyrrolidone, yielding modified products. This example alsodemonstrates the lability of the stabilizing groups.

To two reaction vessels provided with stirrers for continuous agitationthere were added about 130 parts of water. Under continued agitation thefollowing ingredients (parts by weight) were added in the orderindicated to the respective vessels:

(A) Sodium hydroxide 0.8 part, corn starch 100 parts, andN-vinylpyrrolidone 10mm.

(3) Sodium hydroxide 4.0 parts, sodium sulfate 40 parts, corn starchl00'parts, and'N-vinylpyrrolidone 10 parts.

As may be seen in Table No. l, the products showed various degrees ofsubstitution (D.S.). Samples cooked at pH 7.0 indicated stabilization inruns A and B.

The cooks at pH 3.0, however, resembled non-treated corn starch ofcomparable viscosity. The stabilized products, or those exhibitingremarkable non-congealing character of their cooks, as compared tonon-treated base, also exhibit an increase of nitrogen content.Presumably, this nitrogen increase results from the introduction of theethyl pyrrolidone groups.

The results indicated that the substituting groups are labile to cookinga low pH (pH 3.0). The lability of these groups was also confirmed bythe experiment described below.

About 50 parts of sample B above were suspended in about 75 ml. water(tap) to whi'chthere was added one part of sulfuric acid. The pH of theresulting mixture was about 1.7. The mixtures were agitated at about 25C. for 16 hours. Then the starch product was recovered byneuitralization to pH 7, washingand drying. The product lost all itssubstituted nitrogen and its cooks rese'mblednontreated corn starchcooks of comparable viscosity (nitro- "gen dropped to 0.06% from 0.19%,dry basis). This in dicated that all stabilizing and inhibiting groupswere removed by this treatment and proved the lability of these groupsto acidic treatment.

' EXAMPLE II This example illustrates reactions of N-vinylpyrrolidonewith some native starches over prolonged periods of time.

The following materials were added to tap water with agitation in theorder and amounts as indicated: (throughout the course of addition andreaction the pH was adjusted to 3.0).

Sample number Tap water, parts 750 625 625 Sleigh: (1) (2) P t to e o aP r is 500 500 500 10 N-vinylpyrrolidone, parts 100 50 50 TABLE NO. 2

Reaction Nitrogen time (percent Description of cold cook, (hrs.) drybasis) D.S. pH7.0

Thin, opaque fluid. In- 22 6 eompletedispersions.

Moderately heavy, cohe- 22 0:021 s1ve,clearflu1ds.

EXAMPLE III This example illustrates reactions of N-vinylpyrrolidonewith waxy maize by contacting the starch with the reagent in aqueousmedium and also in the course of drying.

Three aqueous suspensions of 200 parts waxy maize in 250 parts watereach were prepared and mixed with the following amounts ofN-vinylpyrrolidone and at pHs as indicated:

Parts of N-vinyl pH of the Sample pyrrolidone mixture The resultingmixtures were agitated at about 40 C. for five hours. At the end of thisperiod the pHs of mixtures read 2.8, 3.3 and 3.8 respectively. At thispoint the products were filtered and air dried without washing. Foranalysis, small samples were taken and each was adjusted to pH 7.0. Thenthese samples were thoroughly washed by resuspension and analyzed fornitrogen content. As may be seen in Table No. 3, the reaction efficiencyis greatly improved by this procedure and was best at pH 3.

TABLE N 0. 3

Nitrogen (percent dry basis) D.S.

EXAMPLE IV hydrochloric acid. About 15 parts of sodium chloride and 10parts of N-vinylpyrrolidone were added to this slurry and the resultingmixture was agitated at 40 C. for 4 hours. After the reaction the pH ofthe mixture was 3.0 and was adjusted to 4.5 with dilute sodium hydroxidesolution and the product recovered by washing and drying as described inExample II.

Analysis indicated that the nitrogen content of the product had beenincreased to 0.45% dry basis.

EXAMPLES V'IX These examples illustrate reactions of N-vinylpyrrolidonewith various starch bases at elevated temperature.

Corn starch converted by acid treatment to a WP of 65, high amylose corncontaining about 70% amylose, and waxy maize containing less than 2%amylose were reacted as described below:

The reaction formulations are given in Table No. 4.

TABLE N0. 4

Examples V VI VII VIII IX Thin boiling (acid fluidity) corn starch (WF65) 1 High amylose corn 60 50 Waxy maize. 200 Water 125 75 75 250 Sodiumsulfate" 60 60 40 40 N-vinylpy'rrolidone 20 20 25 25 20 pH adjusted to4. 0 5. 5 4. 5 6.0 2. 8

In Examples V through VIII the reactions were carried out by suspendingthe starch in the indicated amount of sodium sulfate and adjusting theslurry to the indicated pH, while ading the reagent. The resultingmixtures were placed in constant temperature baths and agitated asfollows: In Examples V and VI the reactions were carried out at 52 C.over a period of 16 hours and those of Examples VII and VIII to 100 C.over a period of 2 hours. Then each mixture was adjusted to a pH of 5.0by adding dilute acid or sodium hydroxide solution, as required. Themodified starches were then recovered by washing the reaction productsessentially free of any salts and drying to a moisture content of about12 percent.

In Example IX the reaction was carried out by suspending the starch inwater, adding the reagent and adjusting the pH to 2.8 with dilute HCl.After about 10 minutes the starch was recovered by filtration, dried toabout 3% moisture, and heated at 200 C. for 5 hours. A brown dextrinlikeproduct resulted.

The products were analyzed for nitrogen content and evaluated by cookingas in Example I. The results of the evaluation are described below.

Example V: (0.44% N, D.S. 0.053) the cold cook at 15% starch solids wasa thin, cohesive, semi-clear fluid.

Example VI: (0.062% N, D.S. 0.008) The cold cook at 15 starch solids wasa heavy chunky mass resembling the untreated starch base.

Example VII: (0.059% N, D.S. 0.073) the cold cook at 10% starch solidswas thinner and more dispersed than the starch base, but still opaqueand syneretic.

Example VIII: (0.59% N, D.S. 0.073) The cold cook at 10% solids had thesame properties as that of Example VII.

Example IX: The product was completely soluble in cold water at 50%solids, giving a thin, dark dispersion.

EXAMPLES X-XV These examples illustrate the preparation of additionalstarch products of this invention by means of an aqueous system.

The procedures employed in preparing these starch products wereessentially the same as described in Example 1, except the corn starchwas replaced by a particularly treated starch in each instance. Alsovarious salts were substituted for the sodium sulfate wherever a saltcatalyst was employed. The said particularly treated starchesarevdescribe d as folows:

(a) A thin boiling, corn starch having a water fluidity (WF) 01. about.75, obtained by oxidizing the starch with sodium hypochlorite.

(b) Corn starch dextrin (white) prepared by. heat conversion.

(c) Acetylated native corn starch.

(d) Cornstarch having sulfonato-succinate groups prepared according tothe method set forth in Example I of assignees U.S. Pat. No. 2,285,727.

(e) A thin boiling waxy maize (WF of about 85) having octenyl succinatehalf ester groups.

(f). Corn starch having sodium phthalate half-ester groups. Compositionsof the reaction mixtures employing the above described treated starchesare set forth in Table 5 below. Al l' concentrations are in parts, byweight, unless specified otherwise. i

TABLE NO. 6

1 Example N o.

. Ingredient X XI XII XIII XIV XV Starch base (100 parts) a b c d e fWater 130 60 130 130 60 130 EthanoL 80 80 Potassium sulfate 30Cyanoguanidine 30 Magnesium sulfate t 30 Ammonium thiocyanate 30 EDTA---I Vinylpyrrolidone I0 10 10 10 10 10 pH 3 0 3.0 3.5 4.0 4.5 3.5

'Disodium salt ethylenediaminete'traacetic acid.

The prepared compositions were first agitated for 17 hours at40" C.,neutralized to pH 5, filtered, washed and'dried. The resultantmodifiedstarches obtained as the. dried reaction products each had amoisture content of about 8 percent of the total weight. Evaluationprocedures were similar to those of Example I, except for Examples XIand XIV. These products, due to the tendencies of the starch base toswell in cold water, were washed and filtered in aqueous-alcoholsolution. Thereafter, using the Kjeldahl method, the extents of thereactions were determined. The respective nitrogen content analyses wereas follows: (X)v 0.20, (XI) 0.11, (XII) 0.22, (XIII) 0.19, (XIV) 0.10,and (XV) 0.20.

Thus, it may be seen that various types of modified starches may be usedin this invention. Although different starch bases reacted to diiferentextents, a reaction occurred in every instance.

EXAMPLE XVI This example illustrates the preparation of a stabilizedstarch product of this invention by means of a dry process.

Approximately 100 grams of corn starch were suspended in 125 ml. ofwater, and the slurry was acidified to a pH of 3.0, filtered and driedto a moisture content of 8%. A reagent solution comprising about 10parts of vinylpyrrolidone dissolved in 22 parts of water and having a pHadjusted to 3.0 by the addition of 7.2 parts of phosphoricac'id'wasthen' sprayed onto the dried starch as it was being agitated.Agitation was continued for 2 hours, whereupon the resulting mixture wasdried and heat reacted in a forced air oven set at 130 C. over a periodof 3 hours. Thereafter the starch product was cooled, washed andrecovered in the manner described in Example I. The dried yellow powderthus obtained had a BS. of 0.046 asindicated by a nitrogen content of0.58 percent.

A cooked dispersion of this stabilized starch, unlike th-atof acontroldispersion which had been prepared using an untreated, identical starchbase, exhibited stabilization which could be removed by heating in acid.

. EXAMPLE XVII V This example illustrates the effect of varying certainreaction conditions or the concentration of the particular 10 catalystused in the preparation of these modified starch products.

(A) Variation in Reaction Time-Using a method similar to that of ExampleI, an additional quantity of N-vinylpyrrolidone reacted corn starch wasprepared as follows:

One hundred parts of corn starch were suspended in parts of watercontaining 40 parts of sodium sulfate, and the mixture was stirred. Thenthe pH of the mixture was adjusted to 3.0 by the addition of dilute HCl.Thereafter 10 parts of N-vinylpyrrolidone were stirred into the mixtureslowly, and the reaction was continued for several days. Homogeneoussamples were withdrawn at intervals of (a) 16, (b) 24, and (c) 116hours. Starch products of each sample were then recovered in the mannerset forth in Example I. Also an additional sample was prepared byresuspending 1 part of (a) in 2 parts of water and stirring thesuspension at pH 11.5 for 16 hours, whereupon the product, (d) wasrecovered in the aforesaid manner.

Cooks were prepared from the air dried products of each of the abovedescribed samples. Then, repeating the evaluation procedures employed inExample I, the degree of substitution and stability of these productswere evalu- (B) Variation in the amount of salt catalyst.-The methodemployed in Example I was repeated in the pieparation of a series of thetypically modified starches of this invention, except the amounts of theneutral salt were varied. In each of the initial samples there wascontained, in addition to the corn starch and 10 percent of theN-vinylpyrrolidone based on the amount of the said starch, a variedquantity of sodium sulfate. After the addition of all the ingredients,the mixtures having pH levels adjusted to 3.0 were agitated at 25 C. forabout 17 hours. Thenthe resulting suspensions were neutralized to a pHof 7.0 with a 3 percent sodium hydroxide solution. The strach productswere then recovered by filtering, washing, and drying. The dried starchproducts having a moisture content between 10 and 12 percent of theirtotal weight, were then tested by cooking according to the procedure ofExample I. The colloidal properties of the resulting cooks were thencompared. Results are set forth in Table VII below.

1 Similar to Example I, except sodium sulfate was not used.

As indicated in the table, samples made using greater amounts of thesalt catalyst exhibited higher substitution.

EXAMPLE XVIII This example illustrates the usefulness of a cyclicN-vinyl imide in the preparation of a modified starch typical of thisinvention.

In this case, the particular starch was modified with N-vinylsuccinimideas follows:

50 parts of corn starch were suspended in an aqueoussalt solutioncomprising 62 parts of tap water and 20 EXAMPLE XIX This exampleillustrates the usefulness of a cyclic N-vinyl imide in the preparationof a modified starch typical of this invention by a reaction in aqueousacetone.

In this case, the starch was modified with N-vinylphthalimide using themethod described in Example XVIII, except a 1:1 aqueous-acetone mediumwas employed and the amounts of the ingredients were as follows:

Parts Corn starch 100 Water 125 Acetone 125 NA SO 30 N-vinyl phtahlimide20 pH 3.0

Upon adjusting the pH of the agitated mixture to 7.0, the modifiedstarch was recovered and evaluated in the manner set forth in Example I.The dried product had a nitrogen content of 0.46 percent, by weight,thus indicating a D5. of 0.064.

EXAMPLE XX This example illustrates the usefulness of an N-vinyl cyclicurethane in the preparation of a modified starch typical of thisinvention.

The procedural steps of Example XVIII were repeated, except 20 parts ofN-vinyloxazolidone was used in lieu of the N-vinyl succinimide, and thereaction was carried out at pH 3.0 instead of 6.2. The N-vinyloxazolidone employed herein was prepared according to the methoddescribed by E. K. Drechel, J. Org. Chem., 22, 819.

The present modified starch had a nitrogen content of 0.17 percent,based on the total weight, which corresponded to a D8. of 0.02.

Summarizing, it is thus seen that this invention provides novel,modified starch products, as well as processes for their preparation.Variations may be made in proportions, procedures and materials withoutdeparting from the scope of this invention defined in the followingclaims.

We claim:

1. A process for preparing a modified starch comprising reacting starchin an aqueous or aqueous-based medium at a pH between 2.0 and 7.0 with aN-vinyl compound selected from the group consisting of N-vinylamides, N-vinyllactams, N-vinylimides, N-vinylurethanes and N- vinyloxazolidones,wherein the nitrogen to which the vinyl group is attached is adjacent toat least one carbonyl group, for a period of from 2 to 17 hours at atemperature from to 180 C., said N-vinyl compound being present in anamount from about 0.01 to 100 percent, by weight, or starch.

2. A process according to claim 1 wherein said N-vinyl compound isN-vinylpyrrolidone.

3. A process according to claim 1 in which the reaction medium is amixture of water and a water miscible organic solvent.

4. A process according to claim 1 wherein said N-vinyl compound ispresent in an amount from about 3.0 to about 50 percent, by weight, ofthe starch.

5. A process according to claim 4 wherein there is also present up toabout by weight, of the dry starch of a water soluble neutral saltselected from the group consisting at neutral alkaline and alkalineearth salts.

6. A process according to claim 5 wherein said salt is selected from thegroup consisting of sodium sulfate, magnesium sulfate, and mixturesthereof.

7. A modified starch produced by reacting starch in an aqueous oraqueous-based medium at a pH between 2.0 and 7.0 with a N-vinyl compoundselected from the group consisting of N-vinylamides, N-vinyllactams,N-vinylimides, N-vinylurethanes and N-vinyloxazolidones, wherein thenitrogen to which the vinyl group is attached is adjacent to at leastone carbonyl group, for a period of from 2 to 17 hours at a temperaturefrom 10 to 180 C., said N-vinyl compound being present in an amount fromabout 0.01 to percent, by weight, of starch.

8. The modified starch of claim 7 wherein the N-vinyl compound ispresent in an amount from about 3.0 to about 50 percent, by weight, ofthe starch.

9. The modified starch of claim 8 wherein the N-vinyl compound isN-vinylpyrrolidone.

10. A process for preparing a modified starch comprising:

(a) mixing a starch with an aqueous or aqueous-based N-vinyl compoundsolution having a pH between 2.0 and 7.0, said N-vinyl compound selectedfrom the group consisting of N-vinylamides, N-vinyllactams,N-vinylimides, N-vinylurethanes and N-vinyloxazolidones wherein thenitrogen to which the vinyl group is attached is adjacent to at leastone carbonyl p,

(b) drying the impregnated starch, and

(c) heating the dried starch at a temperature between about -200 C. fora period ranging from A to 4 hours.

11. The modified starch prepared by the process of claim 10.

References Cited UNITED STATES PATENTS 3,095,391 6/1963 Brockway et al.260l7.4

DONALD E. CZAJA, Primary Examiner M. I. MARQUIS, Assistant Examiner US.Cl. X.R.

260l7.4, 77.5 B, 77.5 BB, 233.3 A, 233.5

